1. Field of the Invention
The present invention relates to a medical X-ray imaging apparatus.
2. Description of the Related Art
An image intensifier-TV system is especially utilized for fluoroscopic radiography apparatus in the area of diagnostic imaging using a medical X-ray image capture apparatus.
FIG. 1 illustrates an example of an image intensifier (hereafter “I.I”)-TV system in the past. First, a subject P is irradiated with X-rays from an X-ray tube 11be through an X-ray aperture 2. Then, the transmission X-rays transmitted through the subject P are detected by a detection unit 3, and converted to an image signal, and the converted image signal is displayed as an image on a monitor 5 via an image processing means 4.
The X-rays with which the subject P is irradiated are placed via the X-ray aperture 2 so as to irradiate only a predetermined region that is required for capturing an image. The detection unit 3 converts the transmission X-rays to an optical image of visible light by I.I 3a, and guides the converted optical image to a television camera 3c via an optical system 3b, where the optical image is converted to the image signal.
The image processing means 4 converts the received image signals to digital image data. The image processing means 4 performs zoom-in and -out of the image, displacement of the image position and various computations including addition and subtraction of the image, and processing of the image. Further, a record unit 6 records and stores the digital image data before or after processing. It is possible that the record unit 6 stores a moving image which is captured by irradiating the subject P with the continuous or pulsed X-rays, or stores a still image which is captured at arbitrary timing by observing the moving image.
As mentioned above, the area which can be captured by the transmissive X-rays transmitted through the subject P impinging upon an entry surface 3a′ of the I.I 3a of the fluoroscopic radiography apparatus is called a visual field size. The maximum visual field size of the normal I.I 3a is determined by the bore diameter and the visual field size can be set by switching a visual field size in a stepwise fashion. The size of the area to be captured is determined by switching the visual field size for capturing the subject P.
Further, it is possible to obtain an enlarged high-resolution optical image by setting a small visual field size. For an example of the I.I 3a, the visual field size can be switched among the sizes of 12, 9, 7.5 and 6 inches. In this case, if a 6-inch -visual field size is utilized, it will be possible to perform image capture at a magnification of four times the magnification (resolution) possible with a 12-inch -visual field size. Recently, a high resolution solid X-ray detection unit is proposed using a FPD (Flat Panel Detector) in lieu of the detection unit 3.
Japanese Patent No. 3066944 shows a method of acquiring the X-ray image of the subject as digital data by converting the transmissive X-ray amount transmitted through the subject to an electrical signal, where the subject is placed between an X-ray source and X-ray sensor by using FPD Japanese Patent No. 3326914 introduces an X-ray fluoroscopic apparatus which can perform an enlargement process by detecting that the image size, which is displayed on the monitor, is smaller than a predetermined size. Japanese patent No. 4042414 also indicates a medical image processing apparatus which performs a reduction process so as to leave the region of interest.
Further, Japanese Patent No. 2786849 introduces an X-ray diagnostic apparatus which can appropriately visualize an X-ray image corresponding to a captured portion and each of fluoroscopic modes and capture modes. Japanese Patent Laid-Open No. 2005-124620 also introduces an X-ray fluoroscopic apparatus which can set aperture information in a trigger so as to obtain a requested image. Further, Japanese Patent No. 3554172 shows a radiography capture apparatus which extracts the region of exposure field from the image fully readout, and performs the image readout according to the extracted exposure field information.
However, the apparatus as mentioned above has the following problems: As for capturing the subject P, in the fluoroscope process of positioning the objective portion to be captured, a wide region and low X-ray amount are desirable and a resolution and frame rate may be compromised in some degree. In the fluoroscope process of positioning the objective portion to be captured, a high resolution and high frame rate are desirable. Once the region is established, the image in a narrow region may be often allowable. Further, in some spot captures where fluoroscopic capture, serial radiography or still image capture is performed, a high resolution may be disabled and the low frame rate may be allowable.
In any capture, the captured region of the subject P is desired to flexibly be set. For example, a clearer and higher S/N image is required when specifying a desired region (the region of interest) for fluoroscopic capture of the objective portion or spot capture using the wide region of the captured image when performing fluoroscopic image capture. For this purpose, the above setting is required when the region of interest is determined by gradually narrowing the region and capture with increasing the irradiated X-ray quantity or increasing the resolution. However, in such capture, there is a problem in that the operation becomes complicated due to the condition of X-ray irradiation, the setting of the X-ray aperture and the setting of binning having to be performed independently. Further, there is the problem that it is difficult to immediately determine whether or not the binning setting should be changed using the image information displayed on the monitor.